Modeling And Stability Analysis Of Train-network System Considering Broadband Harmonic Coupled Phenomenon

With the advantages of rapidity,environmental protection,stability and comfort,highspeed trains have become one of the most popular transportations in our country.It is very important to ensure the safe and stable operation of trains.As more and more trains are connected to the traction network,broadband oscillation phenomena often occur,including low frequency oscillation,harmonic resonance and harmonic instability.This phenomenon deteriorates the power quality of the traction network and seriously endangers the safety of train operation.Therefore,it is of significance to analyze the harmonic coupling relationship of the train-network system and explore the influence of different parameters on the broadband stability of the system.However,the effects of different parameters on system stability over a wide frequency band have not been uniformly analyzed by the reported modeling methods.Based on this,this paper takes the high-speed train-traction network coupling system as the research object,and aims to establish a unified model,which is suitable for broadband oscillation analysis.The specific research contents are as follows:Firstly,based on the linear time invariant(LTI)theory,the transfer functions of the second-order generalized integrator(SOGI)and the phase-locked loop(PLL)in the dq coordinate system are deduced in detail while ignoring the switching characteristics of the system.Thus,the impedance models of the rectifier and its control system are established.On this basis,the dq impedance models of the train and traction network are built.The dq impedance measurement method is used to verify the accuracy of the model in the low frequency band.Secondly,the frequency of broadband oscillation often exceeds 1/2 of the switching frequency,which is difficult to be accurately analyzed with the dq impedance model.To address this issue,the harmonic state space(HSS)model of the rectifier under open-loop and closed-loop control are established based on the linear time periodic(LTP)theory in this paper.The small-signal impedance model based on HSS of the train system is also established,and the accuracy of the model is verified by the single-phase impedance measurement technique.Meanwhile,the model is utilized to reveal the frequency coupling relationship inside the traction rectifier and the interaction between the traction network and the train,which provides the theoretical basis for the broadband oscillation problem of the system.Then,the dq model and the HSS model are respectively used for the stability analysis of the train-network coupling system,and the influence of electrical parameters and control parameters on the system stability is explored.The results of the frequency domain analysis are consistent with the time domain simulation.It illustrates the applicability of the dq impedance model based on LTI theory for stability analysis at low frequencies.At the same time,the analysis results also show that the impedance model based on HSS is suitable for stability analysis in a wide frequency range.The problem that the models are not unified is solved when different oscillation phenomena are analyzed in the current research.Finally,a low-power experimental platform for the equivalent train-network system is built for verification.And the impedance of the rectifier and its control system in AC side is measured by a frequency response analyzer.The test results match the theoretical model well,which verifies the accuracy of the HSS model established in this study.Moreover,the phenomenon of low frequency oscillation is reproduced by using this platform.The influence of parameter changes on low-frequency stability is consistent with the theoretical analysis results,which further indicates the correctness of the train-network stability analysis based on the HSS model.